That's an interesting point. I've never really thought of it that way. You're right, it has the tendency to work out more for those who are already excelling in the game, but I guess it would depend on what kind of guild you join.
In my experience though, no matter what game you play the guilds will always come into play. So, a lot of times, it will be better to be in one. It's still to early to tell, but looking at the way guilds are designed for the Splinterlands, though, I think the main thing that players need is activity. As someone else has mentioned, it doesn't seem to be designed for casual players.